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Reiuued July 27, 1943 ALLOY James M. Lolir, Morristown, N. J., assignor to Driver-Harris Company, Harrison, N. J., a corporation of New Jersey No Drawing. Original No. 2,005,431, dated June is, 1935, Serial N 748,084, October 12, 1934. Application for reissue April 24, 1943, Serial This invention relates to and more particularly to alloys for electrical resistance units.

In the manufacture of electricaljresistance units, an alloy having the property of resisting oxidation at high temperatures is essential. The alloy forming the subject matter of my invention are characterized by the ability to resist oxidation and by a prolonged life, exceeding that of other known alioys,' when used under high temperature conditions.

While nickel-chromium and nickel-chromiumiron alloys having the ability to resist oxidation at high temperatures are known, their period of usefulness in service is often not as long as desired. I have found that the addition of small quantities of calcium, zirconium and aluminum to such nickel-chromium alloys greatly increases their period of life when employed under conditions where they are subjected to high temperatures. The alloys forming the subject matter of the present application may also contain small quantities of either silicon or manganes or both of these elements.

In carrying out my invention I add small qu titles of calcium, zirconium and aluminum, with or without silicon or manganese to nickel-chro- Claims. (oi. 15-170) limits:

Percent Calcium .01- .20 Zirconium .01- .50 Aluminum ill-1.00

mium or nickel-chromium-iron alloys. The nickel-chromium alloy most generally used in the art consists of 80 parts of nickel and 20 parts of chro mium and I find it advantageous to add the other.

metals mentioned aboveto nickel-chromium alloys of substantially these proportions. The proportions of nickel and chromium in th alloy may be varied. Thus the chromium content may be from 15 to 25 percent and the balance nickel.

Likewise the most generally used proportions of nickel, chromium and iron in nickel-chromium-iron alloys is 60 percent nickel, 10 to 15 percent chromium and the balance iron and I find it advantageous to employ substantially these proportions of those ingredients, adding the calcium and zirconium. These proportions may also percentages herein stated and the balance nickel.

If manganese or silicon are employed, they may be used within the following limits:

Percent Manganese -2 0.02-2.0 Silicon 0.20-2.0

Th preferred proportions of the alloying agents are as follows:

Percent Calcium .03 Zirconium .25 l inu .07- .38 Manganese 0.05-1.0 Silicon 0.40-1.0

Nickel-chromium and nickel-chromium-iron alloys containing the above ingredients within the proportions given have been found by tests to have a greatly increased period of life when exposed to high temperatures. For the purpos of determining the life of such alloys at high temperatures I have tested them by the method 'of test outlined in "Tentative accelerated life test for metallic materials for electrical heating," of the American Society for Testing Materials described in vol. 29 of the Proceedings of the Thirty-Second Annual Meeting of the American Society for Testing Materials, beginning on page 613. The method is substantially as follows:

.A sample of the wire to be tested, free from kinks, approximately twelve inches long and of about .025" diameter, is mounted vertically on the test board, the upper end being held in position by means of a suitable binding post. A 10 gram weight is attached to the lower end or the specimen. A short piece of wire is attached to the 10 gram weight and projects downward into a cup of mercury where it may move freely up and down. A rheostat and an interrupter are connected in series with the specimen to the power supply. The test is run on constant temperature at a standard temperature chosen for the alloy under consideration for the first twentyfour hours. Thereafter it is run on constant voltage to the burnout. The life in hours up to a 10 percent increase in resistance is known as useful life while the life to the burnout is known as total life. Throughout the test the power is on two minutes and 01! two minutes. This is accomplished by means of an interrupter.

In testing the alloys 01' my invention according to the above described method a reference sample composed of 80 percent nickel and 20 percent chromium and no alloy additions having an approximate lii'e of 90 hours was used. This value is considered as 100 percent and the useful life of the samples tested is determined in corresponding percentage values. In the following table the results obtained with samples containing calcium, zirconium and aluminum are given.

It will be noted that the useful life of such samples is from 575 percent to 795 percent of the standard sample. When calcium, zirconium or aluminum alone was added to a nickel-chromium alloy of the same composition, in all cases less than 200 percent. 1 The use of calcium, zirconium and aluminum therefore greatly increases the useful life of the alloy for electrical resistance purposes where the wire is exposed to a high temperature.

In the alloys referred to herein, small amounts of phosphorous and sulphur may be present as impurities. The nickel may also contain about 1 percent of cobalt.

Having thus described my invention, what I claim is: I

1. A nickel-chromium alloy containing 15 to 25 percent chromium, .01 to .20 percent calcium, .01 to .50 percent zirconium and .01 to 1 percent aluminum, balance nickel. v c

2. A nickel-chromium alloy containing 15 to 25 percent chromium, substantially .03 percent calcium, substantially .20 percent from .07 to .38 percent aluminum, balance nickel.

3. An electric resistance element comprising 15 to 25 percent chromium, .01 to .20 percent calcium. .01 to .50 percent zirconium, .01 to 1 percent aluminum, balance nickel.

4. An electric resistance element comprising 15 to 25 percent chromium, substantially .03 percent calcium, substantially .20 percent zirconium, from .07 to .38 percent aluminum, balance nickel.

JAMES M. norm.

the useful life was zirconium and 

